The present invention relates to device and method for shift control in an automatic transmission, and more particularly to device and method for shift control that is adapted to reduce shift impact.
In general, a vehicle automatic transmission is mounted with a shift control device to automatically adjust the shift ratio in relation to running speed and load of the vehicle. The shift control device controls a plurality of clutches and brakes cooperating with the gear train in actuated or non-actuated states to adjust the revolutions at the output end of the planetary gear device.
FIG. 3 is a graph illustrating changes in turbine revolution during the up-shift control process in the power-on state in a conventional shift control device. In the xe2x80x9cpower-onxe2x80x9d state, the vehicle is running due to the driving force of the engine. When vehicle speed and openness of the throttle valve are changed to meet a shift condition while the vehicle is running, the shift control device detects revolutions at the transmission output shaft before the shift in order to calculate turbine revolution prior to shifting (Nti). The shift control device detects and calculates the turbine revolution in real time even while the shift occurs (Nt). The shift control device also controls a solenoid valve in the hydraulic system of the automatic transmission to allow the turbine revolution (Nt) thus calculated to be changed in the same pattern as shown in FIG. 3. Furthermore, the shift control device controls the solenoid valve to maintain turbine revolutions after shifting (Ntj).
In other words, the shift control device controls the solenoid valve to cause the turbine revolutions (Nt) to be decreased at a higher rate of change during the first step in the shifting process. Thereafter, the shift control device controls the solenoid valve to cause the turbine revolutions (Nt) to be decreased at a lower rate of change by two steps. The rate of change in turbine revolutions is higher at the second step to obtain a swift response upon shifting, and the rate of change in turbine revolutions is lower at the second of the latter two steps to reduce shift impact to the greatest extent possible.
However, one problem in the conventional shift control device thus described occurs when the vehicle wheels slip due to outside influence while shifting is in progress. In this situation, to increase turbine revolutions subsequent to shifting (Ntj), control time (a1), for decreasing the turbine revolution (Nt) to the lower rate of change during the second step, is shortened below a control time (a0) under a normal state, as shown with a solid line in FIG. 4. Thus, when the control time (a1) is decreased, a complete shift control cannot be realized resulting in the generation of shift impact.
The present invention provides a device and a method for shift control in a vehicle automatic transmission adapted to realize complete control, even when revolutions of the output shaft change due to external influences occurring during the up-shift control process, thereby reducing the shift impact.
In a preferred embodiment of the invention, a shift control device includes vehicle run state detecting means, shift control means and driving means. The vehicle run state detecting means detects a vehicle run state variably output according to a run state of a vehicle. The shift control means performs a power-on up-shift control and controls the turbine revolution relative rate of change after shifting during the control process to effect a power-on up-shift feedback control when a predetermined control signal is output to the vehicle run state detecting means in order to receive back a signal detected by the vehicle run state detecting means. Also, a power-on up-shift signal is input to the shift control means from the vehicle by way of vehicle shift mode state output in synchronization with the control signal, throttle valve openness, revolution of the output shaft, engine revolution, shift lever position and acceleration pedal operation state. The driving means controls the supply of oil pressure discharged from an oil pump to perform the shift in response to a predetermined shift control duty signal output from the shift control means.
In a further aspect of the invention, a method for shift control includes effecting a power-on up-shift control when a power-on up-shift signal is input from the vehicle and controlling the relative rate of change in turbine revolutions after shifting in the shift control process to effect a power on up-shift feedback control.